1. Field of the Invention
The present invention relates to a marking method and apparatus for a semiconductor wafer substrate, or for a glass substrate used for a liquid crystal display.
2. Description of the Related Art
In manufacturing a semiconductor device, one or more marks are conventionally formed on the silicon wafer used as the substrate of the semiconductor device by means of laser radiation for the purpose of product identification. This process is usually called laser marking. More particularly, the surface of the wafer is partially melted on a portion where a mark is desired to be made, in this prior art laser marking process, by a beam of laser radiation such as a Nd-YAG laser, so that an uneven surface is formed which can be identified by the naked eye.
When such marks are thus physically formed, the silicon melted from the wafer by the laser radiation is scattered into the neighborhood of the marking region. Some scattered silicon particles will fall onto and adhere to the wafer surface and thereby cool and harden on the surface, while other particles may cool and harden in the atmosphere and subsequently fall onto the wafer surface. As the dimensions of semiconductor devices decrease, decreased yield of integrated circuit chips from the semiconductor wafer substrate, due to such particles becomes a serious problem. In particular, particles adhering to and hardening on the wafer surface, as described above, have become the main reason for decreased yield of integrated circuit chips from the semiconductor wafer substrate because it is difficult for such particles, which are relatively large and securely fixed onto the wafer surface, to be removed in the subsequent cleaning process.
Prior art FIGS. 4A and 4B show a prior art laser marking system wherein a beam of laser radiation 7 from a laser source 1 is directed via mirror 8 onto the surface of a semiconductor wafer substrate 2 mounted on a substrate support 3. A vacuum pump or gas absorber 4 having an inlet port 6 is shown mounted adjacent substrate 2 to remove any gases 5 which may be in the chamber in which substrate 2 is mounted. Particles 9 are shown being generated by laser beam 7 as it marks substrate 2. In this prior art processing procedure, most of particles 9 generated during the laser marking process will continue to stay on the wafer. In one instance, the number of particles and the yield of chips from the wafer substrate were tabulated. Thirty-five (35) particles were found on the laser-marked wafer substrate, and the yield of chips from the laser marked substrate was 60%.
In order to obviate and solve this problem, a new marking method is proposed in Japanese Patent Laid-Open Application No. 183885/1988, wherein, as shown in prior art FIGS. 5A-5C (corresponding to FIG. 2 of this laid-open application), a photoresist layer 12 is initially formed on the surface of semiconductor wafer substrate 2. Laser radiation is then directed toward the surface of substrate 2 covered with photoresist layer 12 to provide a marking 14 on substrate 2, as shown in FIGS. 5B and 5C. By employing this method, particles 9 generated due to the laser marking will fall onto, and adhere to, photoresist layer 12, so that they can be readily removed together with photoresist layer 12 when photoresist layer 12 is removed after the marking process.
In Japanese Patent Laid-Open Application No. 45801/1996, a similar method for removing particles is described, wherein an oxide layer 13 is used as shown in prior art FIGS. 6A-6D rather than photoresist layer 12 shown in the above case.
These prior art marking methods will, though slightly modified as proposed in the above-referred patent applications, also result in decrease in the yield of integrated circuit chips from the semiconductor wafer substrate because the laser radiation also causes the photoresist or oxide layer to be scattered. Further, the particles generated from the wafer substrate when the laser radiation reaches the substrate may, when dropped on the photoresist or oxide layer, melt the photoresist or oxide layer and thereby reach the underlying substrate and become securely bonded thereto, as shown in prior art FIG. 6D, and thus cannot easily be removed during subsequent cleaning.
It would be desirable to provide a marking method and apparatus by which the particles generated during the laser marking process will be inhibited from adhering to the semiconductor wafer substrate causing less particles to adhere to the wafer substrate, thereby increasing the yield of integrated circuit chips from the semiconductor wafer substrate.